[caption id="attachment_154843" align="alignright" width="223"] Sen. Tom Cotton said he'd "welcome" presidential candidates -- including Hillary Clinton -- to sign a controversial letter to Iran .[/caption]

The leader or Iran and Secretary of State John Kerry found one thing in common Thursday: both condemned the letter 47 Republican senators sent to Iran to warn it against a nuclear deal with the Obama administration.

This sort of direct interference with diplomatic negotiations may be unprecedented and the man behind it, Senator Tom Cotton has been in the Senate only two months.

Cotton of Arkansas is so new, he's still working out of a temporary basement office.

And yet with one letter, he made himself known to diplomats worldwide.

Germany's foreign minister called his letter "unhelpful." A French diplomat says he undermined U.S. negotiators. Does that bother him at all?

"Well all we said was the basic facts of constitutional law under our Constitution," Cotton says.

Cotton's response to the negative reaction from U.S. allies?

"Well then maybe we need to send the message to the entire world."

Cotton is a Harvard-educated lawyer who also led troops in Iraq and Afghanistan as an infantry officer - a background that gives him clout with his GOP colleagues.

And it doesn't hurt that he just defeated a longtime Democratic senator by 18 points after serving just two years in the House, where he was known for his hawkish views. He has called the talks with Iran "sham nuclear negotiations."

Would he be very upset if the letter interfered with the negotiation?

"What we all said in the letter is if we don't approve the deal, we won't accept the deal," said Cotton. "We did not talk about the terms of the deal. I personally oppose the terms that President Obama has already foreshadowed."

Those terms include Iran possibly being allowed to keep some of its nuclear infrastructure. Cotton says he personally went from senator to senator asking them to sign on, and despite all of the furor not one of them has told us yet that they regret it.
By CBS News